


Other Minds

by Pearlhart



Category: Shingeki no Kyojin | Attack on Titan
Genre: Alternate Universe, Alternate Universe - Mermaid, Alternate Universe - Modern Setting, Angst, Fluff, M/M, Romance, Scientist Erwin, Scientist Hange Zoë, Scientist Mike, Scientist Petra, Tech expert Nana, enemies to lovers?, mermaid levi, merman levi, merman sex in my fanfic? more likely thank you think
Language: English
Status: In-Progress
Published: 2021-02-24
Updated: 2021-03-07
Packaged: 2021-03-15 14:40:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 15,187
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29685492
Author URL: https://archiveofourown.org/users/Pearlhart/pseuds/Pearlhart
Summary: This is the find of the century. Perhaps even the millennia. Erwin's team is ecstatic to get to work on the only specimen of mermaid that has ever been found and caught. But for each new thing they learn and discover, the heavier weighs the knowledge of what they're doing to the creature.They're faced with a dilemma: listen to their guilty conscience and end their careers, or continue the groundbreaking work at the cost of their hearts.
Relationships: Levi Ackerman/Erwin Smith, Levi/Erwin Smith
Comments: 48
Kudos: 143





	1. Formaldehyde in the tank

**Author's Note:**

> So I was reading this really cute book about octopuses (fic duly named after said book) and I just really wanted to write a merman fic even if it's not mermay yet. 
> 
> ~~may have written the entire 50k fic in one week of manic writing...~~
> 
> Hope everyone are doing okay and is taking care of themselves ❤️

“It's here, it's fucking here!”

The shouts and the door slamming open against the wall happens simultaneously as Hanji rushes into his office, but Erwin has prepared for this. Has been prepraring for it the past month. With no hesitation he jumps up from his chair and it shoots out, tumbling over and crashing into the flowerpot that isn't doing a very good job at brightening up the place. Hanji has already turned back the way they came and their hurried footsteps are muted in the dense bunker turned research facility. They've been hunkering down in it for too long already and now it looks like they won't be leaving it at all. Grabbing his lab coat, Erwin shrugs it on while jogging to catch up with Hanji. He doesn't really need the coat, but he likes how it feels and it is kinda cool how it billows behind him as he runs. Not that he'd ever admit that to anyone, of course.

He's excited. His palms are sweaty, his heart is racing, the nerves in his body are thrumming and he can barely contain his jubilation of triumph. Finally here, the first documented specimen of what they ended up calling the _homo sapiens siren –_ also known as an old fashioned mermaid. The terminology wasn't really Erwin's idea, but it stuck.

Despite his attempts at composure he just can't quell the grin that is spreading wide across his face. Ahead of him, Hanji is doing absolutely nothing to hide their own excitement, hollering and jumping up and down with the typical manic energy that possesses them when there is a new breakthrough. A door to their right bursts open and Mike's sleepy face pokes out, his mouth half open to chide them but it snaps shut when he see their expressions and his eyes widen. It doesn't take him even a second to understand what is happening and any weariness is gone as he runs to catch up with them.

The bunker is big and they have to jog down many a winding corridor and up several sets of stairs before they're in the main holding area, yet their energy doesn't wane for even a moment. Petra is already there together with Nana, writing furiously on her iPad and looking somewhere between scared shitless and ready to chew off her own hand with excitement. The small woman is literally tittering, her teeth chattering with the effort she's spending on trying to clamp down. Nana is communicating into the walkie-talkie and they can all hear the reply she gets: “ _Specimen 01 “rogue orca” loaded safely on the lift, register ID to accept shipment._ ”

Stepping up to the huge lift that once upon a time used to load tanks and military machinery, Erwin now scans his ID and the green lights flare up. They all startle when the sound of the lift jars through the electric silence and Petra lets out a squeaky laugh that has nothing to do with humour. This is their moment, this is when all their names will enter the history books forever. When the entirety of the science world will look upon them and marvel. This is the find of the century. Perhaps even the millennia. And though Erwin would like to take full credit, the fact that the specimen was even found rests all on Hanji.

While Hanji was stationed at the Aquarius Reef Base, they discovered an area that flicked all of Hanji's brilliant neurons into high gear (while Erwin will always respect them, he's also quietly terrified of their chaotic genius). Using an underwater drone, Hanji spent the better part of a year documenting the area, eventually finding traces of what looked like bones. Bones of beings that were undeniably half man, half fish. The mythological creature called mermaid, kappa, kelpie, nøkken. Impossible, but the evidence was undeniable. The photographs finally got the right people to wake up and Project Mermaid commenced and through a long, arduous process finally ended up in Erwin's hands. He'd lobbied for this, harder than he'd ever worked for anything in his life, and here is the result- _finally_.

The craning noise of the lift stops and for a moment they're all holding their breath while waiting for the doors to open. And when they do the sight that greets them is kind of... underwhelming. There's a remote controlled trolley, a tank covered with canvas and five soldiers dressed in black fatigues keeping a steady hand on the ropes. Mike and Nana direct them to where they want the tank to be placed and the operator in charge jumps off, striding towards Erwin.

“That little shit-” the sergeant throws his thumb over his shoulder, indicating the tank, “-maimed several of my men and nearly killed one of them. It better be fucking worth it.”

Furrowing his brow, Erwin is at a loss as to why military men would have been in contact with the mermaid at all. As far as the reports indicated, then the specimen had finally been cornered and captured in a tight passage by several military grade hiPer subs. The part of the report that got Erwin's attention, however, was the intel that there were several humanoids in the area, all described to look like mermaids. They had all fled through the tight passage, except this one- this one had stayed to fight. The mermaid had nearly wrecked two hiPers before the volts sent through its body subdued it.

The tank is finally in its place and Erwin can barely keep himself from running up to it and tearing the canvas off like a child on Christmas.

“It's awake in there so better be careful, doc,” one of the younger boys tells Erwin with a worried pinch on his face.

“Get the canvas off I want to see!” Hanji yells, startling the boys enough that they all swirl around with their hands on their batons. There is nothing of the careful composure that Erwin has tried to affect in Hanji's excitement. They're pulling on the ropes and swearing at themselves when they can't get the knots open. A loud bang has the tank moving under the canvas and everyone takes a step back, even Hanji. “Is that it, is that the mermaid?” Hanji whispers before they jump back towards the tank again.

“Yeah, that's the fucker alright,” the sergeant grouses. His hand is not only on the baton, he's already unfastened it from his belt, ready for whatever threat that's in the tank.

“Either way, we have to get the canvas off sooner rather than later and I'd like to do it while you're here,” Erwin declares, indicating with a flick of his hand for them to get a move on. The boys comply without comment, making the sergeant twitch his moustache in irritation as they expertly remove the ropes. What does the specimen look like? There were photographs in the report, both from the prone body as they hauled it out of the water and of it in the tank, but that won't do it justice. Erwin knows this on an intellectual level, but he has no idea how much until the canvas is pulled off and the tank stands before them unveiled.

The creature, more like a human than Erwin has allowed himself to believe, is coiled in the confines of the tank that barely gives it enough room to stretch in. He's pale, a natural side effect of being a deep-water creature, though his tail is a slick silver, slender, long and sharp like a knife ready to cut. The creature is all business with no unnecessary frills unlike the colourful but sedate fish relaxing by the reefs. This one is made for something else, it is a warrior.

Its torso and appendixes from the waist up are those of a _homo sapiens sapiens_ unsurprisingly; taut and fit- a very healthy specimen Erwin notes with satisfaction. The tresses of black hair that's not contained in a long braid floats around the specimen's head like seaweed. Most interesting. Erwin is hoping Petra is diligently noting all of this down on her iPad.

With the quick assessment of the specimen's overall condition done, Erwin moves his attention to the face and stops dead. His own involuntary gasp is echoed from his colleagues around the room. Most of the mermaid's face is covered by partially applied and bloodied bandages like someone's been in a hurry to cover it up. Even from where he's standing at a distance, Erwin can see that there are inflamed injuries underneath.

“What have you done to it?” Hanji is the first to react, their voice raising into a yell as they dive forward towards the tank and slaps the glass with the palm of their hands.

“It very nearly killed us, is what happened,” the sergeant barks, “I was given the order to bring it in alive- they said nothing about the condition it had to be in.”

“You fucking idiot!” Petra shouts, startling them all, but her small face is pinched in anger and Erwin knows better than to stop her when she's on the warpath. “You absolute fucking moron! How the fuck do you imagine we'll be able to study its psychological response to humans if he's already been _maimed_ by one of us?!”

“So you softies imagine I'll let my boys get chewed up by a fish-monster so that you can have your little plaything?!” the sergeant roars back into Petra's face. She's standing on her tip toes, head tilted back and chin high, looking to all the world like she's ready to take this man nearly twice her size out.

“Do you know how much this project costs? And now you've gone and compromised it!” She yells back. At the mention of the sizeable budget, the sergeant's face pales and he backs away from Petra who takes a step up and pokes him in the chest. “You better write all of this in your report or so help me God, I will- and it won't be pretty!”

“Yes ma'am!” When the sergeant does a salute Erwin has to rub his chin in a ploy to hide his smile. Despite the garish sight in front of him, his team always comes through.

By the tank, Hanji is petting the glass and cooing at the mermaid. The mermaid on its part is scowling at them with its one good eye and with an astonishingly quick move snaps its tail against the glass where Hanji is standing, making them shout out in surprise and falling back.

“How do you imagine we'll be able to treat these injuries?” Erwin questions the room in general. “There is no chance in hell its going to let us close, so we'll be forced to sedate it and we don't even have its bodymass index yet...”

There's a sharp twist of defeat in his stomach and even though that usually lights the fire of stubbornness in him, this time he's standing face to face with a creature that just looks _too_ human. As a marine biologist, Erwin has researched and worked with many kinds of aquatic wildlife and always with the sincerest respect to their lives, but he's never worked on a human. The face staring back at him from behind the tattered and bloodied bandages is too close for comfort. The one healthy eye isn't flickering, isn't desperate, but quietly seizing them all up: calculating. There is keen intelligence there. You don't need weeks or months of methodical research to figure that out. Erwin is pretty sure that with enough time they could have reached some type of accord, but they don't have that time. Besides, Petra is pretty right on the money that now they might never reach that point at all. They have just gotten the specimen and everything has already gone belly up.

Resisting the urge to hide his face in the palm of his hand, Erwin instead starts calculating their options. The only way they're going to treat these wounds is if they get the mermaid sedated, yet they have no idea how much anaesthesia the creature would need or even if its allergic to it. Should they approach the creature like a dolphin or a shark? This particular specimen does not have breasts for suckling, but it is reminiscent enough of a male _homo sapiens_ that Erwin is confident there might be a female sex as well. So, mammal, then... Or?

Stepping up to the tank next to Hanji, Erwin is aware that the mermaid's (merman's?) eye has not left him for the few minutes they've all stood around, speechless and aghast. With that steely gaze on him, Erwin taps his own healthy eye before pointing at the merman's damaged one. There is no real change in the merman's expression, though Erwin wonders if he might just have imagined the narrowing of its eye.

 _Fuck_. This is such a mess.

“We have to restrain it,” Hanji declares confidently. “We can't risk putting it under so we'll have to restrain it.”

“You don't think that might do more damage to it?” Mike objects, “it looks pretty strong, it might struggle until it gets hurt since it's already done so once.”

“I think Hanji is right,” Erwin states, finally seeing the light in the end of the tunnel and points at the soldiers. “We'll have to restrain it and this is your time to redeem this little blunder.”

Turning back to the sergeant, Erwin finds the man looking like he wants to be anywhere but there. But honour is hard to kill and the sharp nod is all Erwin needs.

It quickly becomes apparent that the soldiers had not been exaggerating the fierceness of the merman. With batons and tasers, hooks and rope, they step up to the tank. For a moment they hesitate, but then the mask of resolution falls onto their faces and they proceed with the operation. The merman is lightning quick and Erwin barely has the time to process its movement before it has a good grip of one of the boys who shouts out in surprise. The soldier next to him must have expected the attack and is on the merman in an instant, tasing the arm that has a death grip on her comrade. Erwin can hear the skin sizzle all the way to where he's standing and he is only seconds away from calling the entire thing off. But the merman's momentary setback is enough for them to toss a rope around its neck and pull. While the specimen is distracted by the rope contracting its airways, the rest of the team has enough time to wrap the black ropes around its arms, chest and torso until it is as immobile as it can get without anaesthesia. There is little they can do about the tail though, and Erwin is keenly aware of the danger it poses when he returns to the edge of the tank. The faces of the soldiers are strained, some of them turning pink with the mere effort of holding the ropes tight. If it's gonna be done it has to be done now, and it has to be done quickly.

Erwin doesn't have to motion for his team to get him what he needs, they already know and are on their way. Hurried and harried, Erwin pours copious amounts of antibacterial gel on his hands before putting on surgical gloves. This is so far from ideal as they could get. Climbing up on the trolley, Erwin leans over the edge of the tank and carefully cradles the merman's face with one hand and brushes away the wet strands of hair with the other, cursing himself when he feels that excitement all over again: to be touching this specimen, to be learning about it. This is not the time, there will be time later. Now he has to assess the damage and clean it up thoroughly so that they won't have to do this all over again any time soon.

But even if Erwin is aware of the danger posed by the merman's tail, he sorely underestimated its teeth. In a flash of white and red the merman's teeth have dug themselves into the flesh of his arm. There is pain, but mostly surprise. In the moment of shock, all Erwin manages to utter is a tame, “ _ow_.” And as if this lethal merman is nothing more than a dog, Erwin gives it a quick slap on the head with the flat of his palm in reprimand.

The merman blinks up at him in stunned surprise and lets go. It is too bizarre of an interaction to process and so Erwin puts it on the back-burner.

Now bleeding and taught a sharp lesson in the anatomy of mermen's teeth, Erwin is reminded of the time he worked on viper fish, though they were neither as quick nor as vicious as this specimen. Holding out his bleeding hand, a scissor is immediately given to him without prompting. With a few snips the useless and dirty bandages are gone and Erwin gets a good look at the damage that has been done. At first glance it isn't easy to decide the severity of it. A sharp gash stretches from its brow to the edge of its mouth, swelling the eye shut to such a degree it is impossible to gague if there's been any damage to the eye itself. Erwin snaps his fingers next to the merman's healthy eye and breathes a sight of relief when he can see the eye underneath the swollen lid move. So it is intact and functioning, though only time will tell if it will still be able to see.

It is quite obvious, even to Erwin who has never operated on a human before, that a blunt weapon has connected with the merman's face. He doesn't have to look further than to the baton at the ready on the sergeant's hip to find the culprit. The fact that its skull didn't break open is a miracle. The gash itself... is deep. Erwin will have to suture it and they don't have time for any local anaesthesia, yet the stoic glare on the merman's face has Erwin pretty certain that if anyone could grit their teeth through the pain, it would be this one.

The merman is calm and that worries Erwin more than its energetic trashing. The good eye hasn't left Erwin for a second, not even when one of the soldiers nearly looses his grip on the rope and hurries to tighten it, or when Hanji clatters around with the first aid kit. What is it planning?

“Alright, this is going to be very uncomfortable, but I need you to cooperate,” Erwin tells the merman, more to calm his own nerves than thinking the merman understands the words.

With a tight grip around the merman's jaw in the hopes that it might at least hinder a sudden attack, if not stopping it, Erwin takes the cotton bud seeped in antiseptic. The merman doesn't flinch or otherwise indicate that it feels the sting when Erwin starts cleaning the gash. If they're unable to do anything about this in time the eye will certainly go sceptic and be lost. In worst case scenario it will kill the merman.

Unfortunately the science lab has been built for the study of marine life rather than creatures that are half marine, half human. The skin of the merman's face is soft, the tissue around the eye thin, but the needle Hanji hands him is a cutting needle meant for stitching of leather-like skin. There is no way around it, the stitches will leave behind ugly scars and Erwin feels resentment when he puts the needle to the open wound. The small face in his hand is uncommonly pretty and Erwin has to refocus to be able to go through with the procedure.

The actual sewing of the stitches is over quickly. Muscle memory takes over and all Erwin sees is the gash closing one stitch at a time. There's a moment of hesitation once he reaches the eye, but he solves it by leaving it alone and using skin glue and adhesive tape instead, hoping it will be enough to keep it closed and that the merman will leave it alone.

While the merman's stoic calm had initially worried Erwin, it is soon buried under the relief that the wound is easier to treat than he had thought it would be. Once the waterproof dressing is in place (though Erwin is pretty certain it will be ripped off in not time, the merman being cursed with hands and opposing thumbs), he steps back and down from the trolley. They all heave a sigh of relief as the soldiers hurriedly removes the ropes, eager to get the fuck out of there.

Erwin should have seen it coming. Petra still remains on the trolley, busy putting the first aid kit back in order when the merman moves. In one moment Petra is laughing with relief, the next she's being hauled over the edge of the tank and forced down into the water. The soldier who tasered the merman is the first to react, reaching down into the tank and grabbing Petra's jacket in an attempt to pull her back. But the merman is stronger and all the grip ends up doing is rip the jacket as it pulls her to the bottom of the tank. Erwin doesn't really have time to think before he's climbing in after her.

The merman has a tight grip around Petra with one hand over her mouth and nose, the other around her chest and the panic is shining in her eyes. Bracing his legs against the glass walls, Erwin tries to pry tloose he merman's fingers, but they're unmovable. Between the mounting panic at their lack of time and furious concentration on the task at hand, Erwin dimly thinks that it is a miracle they managed to catch this beast at all. The merman's silvery eye moves from Petra and lands on Erwin, and in an instant everything changes. Petra is thrown to the side and the fingers Erwin had just tried to bend curls around his neck instead. Time stands still as Erwin tries to think. The only advantage he has is his size so that's what he uses. Kicking off from the bottom of the tank he attempts to use the momentum in the water to propel them to the surface, but the merman simply coils its tail and Erwin is pushed further down, his back now against the floor and the merman looming over him. Outside of the tank, people must surely be doing whatever they can to get to him, but that seems like a world away. All that Erwin can focus on is that one eye staring, the feeling of suffocation, the weight on his chest.

He could stab his thumb into the merman's wounded eye. Not even this stoic being would be able to ignore that and Erwin would be released from the murderous grip and yet... he can't bring himself to do it. Can't bring himself to hurt this creature in his care in such a way. Not even when the edges of his vision starts to darken, not even when his chest burns and he knows that in less than a second he won't have a choice- his body will choose for him and he'll gulp down a lungful of water. In just that moment a flicker of surprise flashes across the merman's face and the vice like grip is released. It is too late- Erwin's consciousness is snuffed out.


	2. Pinned exhibition

**Summary for the Chapter:**

> _The merman's silver eye moves from the bucket to Erwin, then back again in an obvious communication for him to stop being an idiot._

The heavy slaps on Erwin's back are hard enough to rouse him and his chest constricts with violent coughs, releasing water onto the concrete floor underneath him. Someone has put him in recovery position and it takes a while for him to regain the control of his limbs- his body too occupied by fighting the foreign substance in his lungs. Erwin had been so sure he'd die it takes a moment for his mind to catch up with the fact that he's still very much alive. Waves of serotonin washes over him and he ends up laughing and coughing up water at the same time until his stomach joins in and his lunch nearly ends up on the floor as well. Rolling onto his back, Erwin stares up at his team with two of them drenched just like himself. Petra is shaking while Mike reminds him of a wet dog.

The specimen!

Still gasping for air while his chest burns for every lungful he heaves in, Erwin quickly turns around to make sure the merman is whole and healthy in its tank. The lid has been safely secured again and the merman looks no worse from wear as it sits on its tail while glaring at the lot of them. Erwin has a feeling that if the merman knew what giving the finger meant, it would be doing it.

“Well, that is quite enough drama from one fish man for my liking,” the sergeant cuts in, signalling for his soldiers to get packing. “If you don't mind we'll be leaving you docs to it, enjoy.”

“No,” Erwin manages to wheeze from his less than dignified position on the floor, “you have to get the specimen into the main tank.”

“What?!” One of the soldiers cuts in, his intense, green eyes widening in surprise. “That motherfucker has nearly killed us several times already!”

“The water is polluted, if it remains in there it will die and we can't very well do it alone, we don't have the manpower to!” It's not often Erwin feels rage, but right now he's ready to take one soldier and beat the other with. “Get the hell to work!”

“Fine, but this is the last thing we do for you maniacs,” the sergeant concedes. The atmosphere is strained as one of the soldiers steers the trolley towards the large tank that has been set up at the end of the hangar.

They'd not been entirely certain of the dimensions needed for a merman, so they'd measured after the size of a great white shark. This merman is quite a bit smaller than that, so on the plus side it'll have more room, but on the negative it will mean a much more difficult time reeling it in.

The trolley slowly raises on its spindly but sturdy legs to the top of the large tank and the four soldiers does an admirable job of tipping it over and removing the lid. It is obvious that they are hesitant to do so, skittish at the thought of releasing the beast again, but they dutifully fulfil their orders. The lid of the tank is opened and it is only for the merman to slide down into its new area, but it remains stubbornly at the bottom of the smaller tank.

“For heaven's sake!” the sergeant barks, “just upend the entire tank and let us get this shitshow over with. Kirstein and Ackerman, you hoist the back end, Jaeger and Arlert, you hold the tank steady.”

The soldiers does as instructed and tips the tank all the way over and Erwin has to admit that he's impressed. That tank is _heavy_. It has the desired effect though- the merman is unceremoniously tossed into the larger holding area and immediately upon release swims to the furthest end. Erwin lets out a long sigh of relief that ends with a coughing fit. This has been more action than he's used to seeing after years working in labs. With the merman safe in its new habitat, the soldiers take their leave without as much as a goodbye and the scientists are left alone with their new miracle.

“Well then...” Hanji is the first to break the silence, but even their endless enthusiasm has been curbed. “These mermaids are nothing like the fairytales, huh. At least not the Disney versions, but I guess the ancient Greeks had a point-”

Now that the adrenaline is leaving Erwin's body he can feel the fatigue take over and his skin is icy cold. Mike helps him off the floor and together with Petra they have no choice but to change into dry clothes.

“Fucking hell,” Mike mutters as they slowly make their way down the corridors towards their living quarters. “I wanted to choke the life out of that little shit.”

“I'm glad you didn't,” Erwin replies, voice still hoarse. “It let me go, you know, just before I blacked out.”

“So it showed mercy despite being put in a life or death situation,” Petra murmurs. “That's a sign of a very deep sense of empathy.”

Erwin's heart skips a beat. What exaclty is it that they've captured and put in a tank?

Some hours later Erwin is feeling a bit better. At least he's dry, though he doubts he'll be able to eat for quite some time. They're all milling about in the hangar unwilling to leave the merman alone in the tank. Erwin has pulled out a chair and sits quietly staring at the merman who in turn has not broken the stare down once. If it hadn't been for the reinforced glass between them, Erwin doesn't doubt that he'd get his throat torn out by those sharp teeth. The bite from earlier has been dressed and is throbbing, reminding him that it could have been so much worse. He's pretty certain the merman has enough power in its jaw that it could have fractured the radius, or at the very least ripped out a good chunk of flesh, tearing sinew and tendons right out and rendering the arm useless. The question is then: why hadn't it? Brutal self defence would only have made sense in this situation.

“Is it hungry you think?” Petra wonders from where she's standing behind Erwin. “It's been in transit for over seventy two hours.”

“Probably,” Erwin concedes, “but I doubt it'll eat anything at the moment- certainly not while we're here.”

“I didn't really imagine it to be like this.” Petra's voice is so soft, Erwin wonders if she meant for him to hear it at all, but he can't help but agree.

The habitat they've created for the merman is quite uninspired. They tried their hand at recreating the area where it was first found; dense sand and rocky, but very little vegetation. It looks bleak in there.

Eventually they've all grown too weary to stay and Erwin knows that sleep and food is crucial for them to stay alert. They'll do the merman a disservice by getting sloppy from fatigue. Hanji volunteers to take the first shift in the surveillance room and is already deep in their notes when Erwin pokes his head in to check on them. They look up and wishes him a good night, but Erwin doubts he'll be able to sleep. At least he'll be giving it an honest try.

Breakfast the next morning is a quiet affair. Everyone seems preoccupied with their own thoughts, staring into space and carefully avoiding each other's gaze. Erwin was the last on the surveillance shift last night and he'd not been able to sleep a wink- just as he'd feared. The other insomniac keeping vigil had been the merman- it had remained unmoving in the same spot the entire night. They'd left some thawed squid and sardines, unsure what it would like to eat, but the merman hadn't so much as sniffed at it. Erwin can't help but worry.

Since they have evidence that there are others of its kind, other mermaids it had been willing to stay behind to protect no less, it is obvious to Erwin that mermaids are social creatures. All animals that fall into the category need their own kind when they've experienced trauma. And there's no doubt that this merman has experienced incredible trauma, both psychological and emotional. Without its kinfolk it is very likely that it will waste away and die, a common phenomenon with any social mammal and there is only two ways to solve the problem: release it or catch more. Though even if they were to get their hands on another of its species, there are no guarantee they wouldn't fight for territory. Just because they're social doesn't mean they're compatible. But too much rests on this project, too much money and expectations, they can't simply go: “ _this is weighing on my conscience, let's just release it again_ ”.

This discovery of the century has put a crushing weight on Erwin's shoulders and he's sickened by his continuous excitement at the prospect of working on the project.

In the hangar the mermaid remains immobile even when the lights are turned on and the humans starts milling about again. They open the ceiling of the tank a fraction to remove the food before it disintegrates completely. The merman doesn't seem to register it at all and continues to stare right ahead as if it has entered a catatonic state.

“This is bad,” Nana declares unnecessarily. They're all aware how bad this is.

Walking up to the glass, Erwin hopes against hope that it will garner some attention from the merman. It had been intently focusing on Erwin all of yesterday, so perhaps his presence will yield the same results today. Nothing.

Hours pass. They pace, write notes, chew their nails, try to feed it something else. Hanji talks to it non stop but Erwin doubts it can hear much through the thick glass. Hours pass into a day, into several days. How long can it stay alive without food? If it hadn't been for the merman occasionally stretching out its tail, Erwin would have worried that it had already died.

Eventually Petra petitions everyone to find a name for it, arguing that they can't keep referring to it as just the “specimen”. Erwin avoids partaking in the endeavour; it already looks too human, behaves too much like them, so a human name will make it ten times worse when it inevitably wastes away.

The lack of sleep and harried nerves are putting everyone on edge and the simple task of naming the merman ends in a fierce argument between Petra and Nana for no reason Erwin can discern. Eventually Hanji breaks it apart and mollify them with the suggestion that they all write down a name and then they'll draw for it.

Erwin doesn't want to hear it, but he can't help it when Petra whoops with joy as she pulls out the name she'd written down: Levi.

A week has passed and Erwin has taken up his customary place in front of the tank. There is little else he can do before the merman dies. At least then they can perform an autopsy and learn _something_. It isn't a comfort.

But while Petra is busy measuring the water pressure, temperature and toxicity in the water, Erwin notices a small change in the merman. Its catatonic stare suddenly focuses on Petra's small shape and Erwin wonders if perhaps her colourful red hair is what is making her a target. After a few moments where Erwin holds his breath wondering what the merman will do, if anything, the steely gaze slowly moves from Petra and falls back onto Erwin again. This is the most the merman has done since the first day and a surge of hope rises in Erwin. Even if its focus is one of aggression, it is so much better than the stasis it has been in the past week.

“I want to go in.” The compulsion hasn't even settled fully before Erwin voices it, but once it is out he knows that's exactly what he wants to do.

“And nearly get killed all over again?” Mike asks incredulous. “I'm not jumping in after you this time.”

“I'm not going fully in,” Erwin amends, “but I want to open the ceiling and climb up to the grates. If it moves too close I'll be able to jump back.”

“It's worth a shot,” Hanji agrees, ever the one to pounce on a dangerous plan.

Preparations are made. Nana tries to persuade Erwin to bring the electric prodder, just in case, but he vehemently disagrees. He is absolutely certain the merman will be able to recognize that device. Instead Erwin brings with him a bucket of live fish as he climbs up the ladder. Along the length of the tank there's a grate for easier access and with the glass ceiling opened about three meters he settles down on it. To Erwin's immense relief the merman has followed the entire progress, finally interested in the goings on around it. Even if this is the extent of today's experiment it is enough to fill them with hope that the case is not entirely lost. Taking one of the fish in an expert grip, Erwin puts his hand in the water so that the fish's movements disturbs the surface. It has to be a familiar sensation for the merman, though Erwin is pretty certain that it is too intelligent to fall for any trap. But it has to be starving.

One moment the merman is sitting in its usual spot, the next a silvery sheen flickers through the water and a heavy weight crushes Erwin's chest. He's been pushed back onto the grate and the merman is above him again, though this time blessedly not under water. Erwin's attention is drawn to the dressing which the merman has not touched much to Erwin's surprise. The scratches that he'd deemed better off healing cleanly without a dressing has already closed and there is very little inflammatory redness. A fist grabs the front of his shirt and Erwin's attention snaps back to the healthy eye. The merman looks ready to rip him apart with its teeth and Erwin isn't doubting that its quite capable of doing so. Yet it isn't fear Erwin feels, but something quite different. Something akin to awe.

From below he can hear his team shout and he hopes against hope that at least Hanji has the sense to stop them from coming up there. The weight of the merman is heavy and Erwin can feel it crush him, can feel the water seep through his clothes, the unrelenting stare digging into him, but the merman has yet to attack. At this point Erwin doubts that it will. What is it that its trying to communicate? A warning? Distress?

“I'm sorry,” Erwin apologizes honestly. The merman's eye flickers down to his mouth before shooting back to meet Erwin's gaze. There is little expression on its face beyond a slight crease of its brows. It is enough to have Erwin's heart pound in his throat. What an absolutely magnificent specimen.

Again, Erwin doesn't have time to process what is happening before the weight is gone from his chest and the merman is gone. The shimmer of its tail disappearing down to the corner it has been occupying. When Erwin turns to the bucket of fish with the intent of releasing them into the tank he finds that it is already gone. With shaking legs and arms, Erwin manages to climb down the ladder without tripping on his own feet and is met by cheers and several pats on the back.

“I can't fucking believe it!” Hanji hollers, “you did it Erwin, you fucking went and just did it!”

Stunned by the close encounter and his success, Erwin stands for a while staring at the merman who is busy catching the fish that's escaping from the bucket. It doesn't look like the humans hold any more interest for it now.

Dinner goes down much smoother than breakfast and Erwin can't help thinking of how the merman had torn into the fish with apparent relish. At least now it won't die of starvation. The creature is a fighter, that is for sure, and a fighter who has avoided killing Erwin twice now.

“When Levi pounced on Erwin I was sure that was the last of him,” Nana declares between sips of wine. They opened a few bottles in order to celebrate the event and while the others are already on their second or third glass, Erwin has hardly made a dent in his. He wants to stay alert.

“I can't believe how lucky you are,” Mike hums, but there's a smile under his moustache. Despite his stoic appearances, Erwin knows he's been as worried as the rest of them.

For the first time since the merman arrived, Erwin manages to fall into a deep sleep. It doesn't last long before he's abruptly shaken awake by an agitated Hanji who unceremoniously rips his duvet off and turns on the garish lights.

“You want to see this Erwin,” Hanji crows. Light is glinting in their thick glasses and even if Erwin trusts Hanji fully, he does worry about them sometimes. But Hanji doesn't have time for Erwin's sluggish response and grabs him by the arm before hauling him up from bed. “Hurry, you old geezer, you'll thank me later.”

Shoving his feet into a pair of slippers, Erwin follows Hanji down the corridor dressed only in his sleepwear, but once he enters the surveillance room and sees what Hanji is pointing at, he's glad he did. From the camera that's placed right inside the tank, inconspicuously hidden by some fake foliage, they have a perfect view of the entirety of the merman's area of movement. The merman is, and Erwin can't believe his own eyes, using the bucket to haul sand over to its corner of choice to build a sort of nesting area for itself.

“I was watching Levi figuring out the use of the bucket,” Hanji tells Erwin in a reverent whisper. “Initially he was placing the fish bones into it, but then decided it was better to bury them and use the bucket for something else.”

It doesn't go past Erwin's notice that Hanji is using both the new name and pronouns for the merman. So it's too late for his crew- they've obviously already grown attached to it. And how could they not? Watching the merman studiously at work Erwin can't help but feel pride. Pride that his merman is so smart, and how messed up isn't that?

The next few days Hanji is busy trying to engage the merman by throwing in various toys that's used to stimulate play in dolphins. The merman scowls at the toys and at Hanji, only moving from its nest when Erwin brings fish. Not wanting to push his luck, Erwin is more careful now, only opening the ceiling long enough to pour the bucket of fish into the tank. It is quite a marvel watching the merman move in the water as it catches its treats, its long tail glinting like steel. Eventually the merman grows annoyed by the accumulation of toys in its habitat and starts throwing them back at Erwin whenever there is feeding time. Getting a ball full in the face should have been annoying, but Erwin can't help but laugh. The accuracy of the aim is uncanny and Erwin writes it all down in his report:

“ _Today specimen 01 grabbed the bucket again and proceeded to put all the smaller toys in it, bringing it back later for me to take. A very direct way of telling us to stop putting things in its habitat, much to Hanji's chagrin_.”

Even if the progress has been astonishing, Erwin is not entirely satisfied. He wants to inspect the merman's wounds properly in order to make sure its healing correctly. Mike does not agree when Erwin airs the idea that he should go back in the tank.

“Levi doesn't want anything to do with us,” Mike argues, “he has made that pretty fucking clear. If you keep pushing him, he _will_ hurt you.”

Possibly it will, but Erwin argues that it is a risk worth taking if the specimen is to remain healthy. Eventually the team caves and Erwin readies himself to go back up there to meet the merman yet again. It is still a gamble, the merman could completely ignore him this time even if he brings its favourite fish. After much trial and error they've landed on tuna which Erwin suspects the merman hasn't actually tasted before, it not being native to the area they caught it in, though it is a possibility that mermaids are migrating animals. Despite the room for error in judgement at approaching specimen 01 again, Erwin can't ignore this when they've finally made contact. There is just too much to learn and discover.

To Erwin's surprise the merman readily swims up to the surface when the ceiling is removed and eyes the bucket with anticipation. This time it won't get the reward right away though, and Erwin suspects the merman will grow impatient quickly. Besides the bucket of tuna, Erwin has brought the first aid kit and it doesn't take long before the merman sees it and its thin brows draw together in that cynical frown.

“We have to look at it,” Erwin explains, pointing at the merman's damaged eye. It isn't like the merman understands, but the humanity in its expression makes talking to it a hard habit to shake. Shock nearly stills Erwin's heart when the merman raises its arm and points at the bucket of fish. Is this a natural way for them to communicate or has it already picked up on the gesture from the humans? With these thoughts churning, Erwin is late to react and the merman's patience has already reached its limits. With only a casual flick of its tail it is by the grate and grabbing after the bucket. Erwin barely has the time to move it out of reach. Taking the first aid kit resolutely into his lap, Erwin states firmly, “first this.”

The merman's silver eye moves from the bucket to Erwin, then back again in an obvious communication for him to stop being an idiot.

“Come here,” Erwin orders, motioning towards himself, “then you'll get your tuna.”

Not convinced, the merman dips down into the water again, only its eyes above the water and its black hair floating around it. It has not braided it again and Erwin thinks it wouldn't hurt to put a comb to it.

“Don't be so stubborn, the quicker you agree to this the quicker you get your food.”

The fact that the specimen shows any interest in the fish at all surprises Erwin- it isn't more than a couple of hours since its last feeding. Perhaps it needs more sustenance than they first anticipated. Or it could just be that it finds hunting fish divertive.

With patience he doesn't really have, Erwin applies the antibacterial gel and puts on his gloves before carefully opening the first aid kit. The specimen narrows its eye, but it has yet to move away. There is no doubt that it understands exactly what is going on and remembers what happened the first night in the bunker. They're at a stalemate. Erwin can wait as long as it takes, but he knows full well that the specimen can too.

Time passes, though Erwin isn't keeping track of how much. The merman moving in the water is a mesmerizing sight and he'd be happy to sit there just staring if he didn't have this important job to do. Then the specimen moves and Erwin braces himself for impact, closing his eyes momentarily waiting for that crushing weight on his chest. When he hears the thud against the grate he opens them quickly to find the merman sitting next to him, lips pursed and eye narrowed. It could easily reach the bucket of fish from there, but its attention is elsewhere. Instead it just sits there, looking for all the world like it does so all the time with its chin raised and one eyebrow cocked critically. The specimen's small frame belies its impossible strength and Erwin has a difficult time comprehending the much smaller creature next to him. This little thing managed to take out five soldiers and nearly kill him twice?

Erwin snaps out of his reverie when the merman starts rummaging through the first aid kit and picks up the small scissor which seems to interest it. When it holds it up for inspection the light reflects on the stainless steel and its healthy eye widen a fraction. The merman must have decided that it's of interest because it tosses it into the water, probably to be looked at further later. When the merman dives right back into the kit, Erwin has to stop it before it steals any more of the supplies. The merman is none too pleased by this if the disgruntled look on its face is anything to go by.

“You'll get to look through it after this, Levi,” Erwin tells him decidedly and slowly lifts his hand towards the small, pale face.

Levi doesn't startle or otherwise pull away from his touch. Is it trust or just the knowledge that he is so much stronger? Whatever the reason, Erwin is grateful when he can carefully brush the long strands behind his ears. They're nothing like the soft ears human have, instead they're covered by flared fins to protect the auditorial canal and to pick up sounds and motions in the water. They're silver grey, like his tail, and gradually turns a dark blue at the tips. Erwin manages to refrain from touching them, but only barely.

With just as much care he starts removing the waterproof binding and concentrates on the wound underneath. A soft sigh of relief escapes him when he finds the stitches intact and no immediate swelling apparent. The eye is still closed shut, but a small slit is visible and Erwin tips Levi's head back to get a better look at it. He doesn't want to force the lid open yet, but the fact that it has healed so quickly in such a short time is promising indeed.

“You're quite amazing,” Erwin praises Levi, but he's merely met with a flat stare. What he doesn't say is how pretty that small, symmetrical face is or how mesmerising the silver eye. Maybe not such a wonder that mermaids got the reputation of luring men to their death if they're all like this.

Satisfied with the progress of the stitches, Erwin cleans them and applies a new dressing. The stitches will come out by themselves eventually so thankfully he doesn't have to remove them. Grudgingly, Erwin lets go of Levi's chin and makes good on his promise to let the merman rummage through the first aid kit again.

After a while Levi grows bored with it and only hangs onto the thimble while discarding the rest as more human trash. Instead he pulls the bucket of fish closer to himself and looks at them for a while, putting a hand in to brush against the smooth scales of the tuna swimming around.

In one moment he's silently petting them, in the next he's holding a struggling fish up to Erwin who startles back at the unexpected gesture. When the merman pushes it demonstratively against his chest, Erwin realises that Levi is trying to give him the fish, but he doesn't know if he should take it or not. Would it be rude not to? The hesitation has Levi clicking his tongue in irritation and the oddly human gesture breaks Erwin's spell. Holding the thimble up, Levi again pushes the fish against Erwin. Of course, the merman is paying for the item. Grabbing a hold of the fish whose energy is quickly draining in its death struggle, Erwin quickly snaps its neck. At least its pain and fear is over and Erwin figure they might as well bake it for dinner. It would be too bad to let it go to waste.

Levi raises his eyebrows at the dead fish, but then shrugs as if to convey that human behaviour is beyond understanding anyway. Done with playing nice, Levi takes the bucket and disappears down into the water again just as quickly as he had appeared. Erwin remains for a while looking down into the water while trying to process everything that just happened. The hangar is completely silent- his team just as at a loss for words as himself.

It isn't until Erwin has climbed down from the tank that he realises he's been thinking of the merman as Levi the entire time. Fuck.

**Notes for the Chapter:**

> I hope everyone are taking care of themselves ❤️ Thanks so much for reading!


	3. Operation theatre

**Summary for the Chapter:**

> _The sound of the door opening and shutting has Levi's immediate attention, his eyes turning towards Erwin and the spectral lights shining from them has him pausing in his steps. Intellectually he knows that it is the tapetum lucidum in Levi's eyes that's giving them that glow, but there is no helping the thousands of years of prey instincts clutching at his cerebellum._

**Notes for the Chapter:**

> Thank you everyone so much for all your kind comments and words! They have really brightened up an otherwise rather dreary week ❤️❤️

“ _Today we brought a comb to specimen 01, otherwise known as Levi, and introduced it to him as a tool to groom himself. He took it, looked at it for a while before throwing it forcefully at Hanji. Petra suggested Levi might be of the opinion that Hanji needed it more than him._

_Eventually, I managed to convince him to sit still while I tried my hand at untangling his hair. There was only a minor scuffle when I accidentally tugged at it too hard, but my attempts at braiding it, however, was met with scorn and in the end Petra had to overcome her fear of the tank to approach him. It might be my imagination, but Levi's brusque mannerisms calms down around her presence. Does he remember what happened between them? Or is her smaller stature less threatening to him? Whatever the reasons he has for calming down, it was a success and Petra was able to braid his hair without incident._

_Afterwards he got something from his collection of things to gift Petra as thanks. It turned out to be the set of keys that I've been looking for- when did he manage to steal those?”_

A month passes, then two. Levi has grown tired of tuna and now only wants salmon. Most of the team has gotten familiar enough with the merman that they all take turns with the feeding or just hanging by the edge of the tank in the hopes that Levi will regale them with his presence. Whenever Hanji shows up he makes sure to be as far away from them as possible and Erwin can't help but feel for the disappointed scientist. They were the one to discover the existence of mermaids in the first place and now they're completely ignored by the one specimen they have.

“Is it because I threw all those toys in, d'you think?” Hanji wonders as they lie on the grate staring morosely into the quiet water. Erwin, who doesn't really want to miss a moment with Levi either, shrugs. He doesn't want to tell them it is probably their loud voice and erratic flailing of limbs that sets Levi's hackles up- so to speak. He feels certain they'll grow used to each other eventually.

Once Hanji finally grows bored and leaves, Levi's dark head pops up from the surface. Erwin has finally been able to remove the dressing and the stitches are healing well. They all exhaled a breath of relief at finding the eye nearly all the way open and the silver coloured iris staring back at them with much judgement. Now he's giving Erwin that exact look and Erwin can't help but smirk back at him. The little merman can be quite a little shit- cold as ice one moment and then wreaking havoc the next. Erwin will never forget the time Mike had been on duty to monitor the water and Levi suddenly upended a bucket of water on him. When Mike roared his outrage up at the merman his reply was merely to drop the bucket as well, the clunk as it hit Mike's head audible in the entire hangar.

“Why won't you play nice with Mike and Hanji?” Erwin asks Levi who is leisurely making his way towards the ladder Erwin is leaning on. There's some distance from the water's edge and up to the ladder, but Levi makes the jump effortlessly despite his muscles having waned from the lack of proper exercise. With the merman hanging from the edge of the tank there's only a few inches between them, but Erwin isn't about to move. He feels pretty certain that if Levi had wanted to hurt him, he would have done so a long time ago. Despite Levi's astonishing intelligence it doesn't seem like there's any duplicity in him. What he wants he tries to get and what he doesn't like he chases away. Mike and Hanji being case in point.

“Hello there,” Erwin greets him, watching the water droplets in Levi's thick lashes. Some of the stitches have come out now and Erwin is sad to confirm that the scarring will be permanent and not too pretty. Will Levi care about that? He doesn't seem vain, though he's particular about his living space. Levi doesn't answer with words, obviously, but rests his chin on the back of his hand and blinks slowly.

“I brought you something,” Erwin continues and fishes the small compact mirror up from his pocket. It is real silver and glints in the light much like Levi's tail when he twirls in the water. Erwin had ordered it off the internet with the idea that he could use it to bribe Levi, but now he just wants to give it to him as a gift, though he hopes that the sight of his own maimed face won't shock Levi too much.

Levi takes the proffered item and stares at it, turning it around with his slim fingers admiring the sheen. Being as clever as he is, it doesn't take long for him to find the latch and work it so that he can open the mirror. The glare of the glass has his eyes grow big momentarily and his lips open in wonder. It isn't until he angles it that he catches himself reflected back and the small startle would have gone right by Erwin if he hadn't been close enough that their arms are touching. Levi is frowning at the mirror as he carefully taps his own cheekbone and sees the movement reflected back at him, then he moves his hand to the wounded side and glides one finger down the length of the ugly gash. Nothing of this is beyond what Erwin expected of his little merman, though his self-congratulatory smile fades when he sees the look Levi gives him. Even if the expression is gone in an instant, Erwin will never forget those silver eyes widening and mouth stretch into a pained frown. Vulnerability, even if only for a moment.

Smacking the mirror shut, Levi cradles it in his hand as he hangs there threading water and rubbing the engraved pattern of roses with his thumb. Though he never speaks, there is something in his body language that conveys silence. Disappointment perhaps? Thinking quickly, Erwin remembers the brutal scar across his own torso from the time he had been dumb enough to approach a great white shark. Some lessons were just learned the hard way.

Climbing all the way up the ladder he sits down on the top step, but Levi doesn't deign him with any attention until Erwin starts unbuttoning his shirt. The scars are old enough now for most of it to have turned white, but the way it covers most of his abdomen always makes for a cool story to tell new partners. Erwin is quietly smug about that. Now Levi is peering at it with his aloof expression back on his face as he moves over in between Erwin's legs to get a closer look. With the available hand not clutching the mirror, Levi pokes at the scar tissue and Erwin is having a hard time not laughing at the tickling. With a deadpan stare that can only convey a “ _are you kidding me?_ ” sentiment, Levi clicks his tongue in the way Erwin has learned means he's exasperated. Quite probably Levi recognizes the pattern of scars as that of a shark and finds Erwin to be an absolute dumbass who managed to get them in the first place. But whatever had occupied Levi's mind now seems to be at least temporarily forgotten.

Levi hangs snugly in between Erwin's legs as he fiddles more with his new gift. It is a very intimate position by human standards, but Erwin is unsure how personal space works for mermaids. Levi seems unconcerned by it, his focus completely on the mirror and Erwin takes the moment to study him better. He can't help but admit that the merman has him enthralled. There's not a moment of the day when he's not thinking about him in some capacity. Of course, it is the endeavour of a lifetime, the apex of their scientific work but- this feels more... personal. The lights glaring down at them as they step onto the stage to receive the International Prize for Biology seems far away now that the creature they are supposed to study is quite literally in his lap.

With a sigh, Erwin brushes the inky strands behind Levi's ear, wondering why the merman got used to him so quickly. The fin covering his ear is plain grey today and Erwin frowns in mild worry. He hopes Levi hasn't caught some type of cold or that his health is otherwise declining. But when he touches it, he finds that it's no colder than any other part of Levi's body. Erwin trails his fingers from the ear and down Levi's slender neck, briefly brushing over the gills and further to his toned shoulders. With a sharp inhale, Levi glances up at him just as his ears turns a brilliant shade of blue. Is he blushing? Levi quickly returns his attention back to his mirror, but by the arch of his brow and slight thinning of lips, Erwin suspects that his composure has been shaken. The fact that Levi still hasn't moved away is what has Erwin's own heart accelerating.

“Erwin, why have you taken your shirt off?” Mike suddenly yells.

Levi is gone with only soft waves left behind before Erwin has the time to reply.

It is 2 am and Erwin is on the surveillance shift. There is no reason to worry that Levi will harm himself anymore, but anything could go wrong from a power outage to the temperature in the tank plummeting. It is as good a time as any to get some paperwork done and Erwin is filling out the report for the day. Not much happened; Levi chased his fish, bullied Hanji and otherwise kept to himself. Erwin hasn't spoken to anyone about it, but he can't shake the feeling that Levi has been more morose since he was given the mirror half a week ago. It had been a silly idea, Erwin should never have gone through with it. Even if Levi isn't vain, then nobody wants to see their mauled face and now Erwin is incapable of giving any comforting words. Again Erwin returns to the nagging thought that they cannot keep Levi isolated from his own kind. It isn't healthy for a mind such as his.

At the moment Levi is doing lazy laps around his tank and Erwin knows he must be missing the currents even more than Erwin misses the breeze outside the bunker. The difference is that Erwin can leave at any time.

Getting up from his chair, Erwin lets his feet carry him to the hangar. It is dimly lit during the night to give a sense of a day and night cycle, but Levi doesn't seem to care much and only takes a few short naps now and again. Ever vigilant, ever ready to fight.

The sound of the door opening and shutting has Levi's immediate attention, his eyes turning towards Erwin and the spectral lights shining from them has him pausing in his steps. Intellectually he knows that it is the tapetum lucidum in Levi's eyes that's giving them that glow, but there is no helping the thousands of years of prey instincts clutching at his cerebellum. In his soft slippers, Erwin doesn't make any sound as he walks up to the tank, but Levi's keen eyes has no problems making him out in the half-dark. The silver in his hand shimmer as he drops what he's holding to the floor of his tank, disturbing the sand into a soft cloud. Erwin doesn't know what to think of the gesture and pretends like he hasn't seen it, moving to grab the controller for the ceiling of the tank instead. His team would kill him if they knew what he's about to do. Even if they've all reached a sort of truce with Levi, none of them trusts the merman to the point where they'd want to be alone with him. And perhaps Erwin is being a moron, but he doesn't care.

By the time Erwin has climbed the ladder and walked onto the grate, Levi is already there waiting for him.

“Hello,” Erwin greets him softly. He still hasn't shaken the habit of speaking to Levi and it doesn't seem like the merman minds it, replying in kind in whatever capacity he can be bothered with despite not understanding. This time he uses his tail to splash Erwin with a bit of water, but not enough to soak him. Becoming wet is par for the course of hanging with Levi and Erwin is quite used to it. Rolling up his sweatpants and taking off his slippers and socks, Erwin settles down next to Levi and they stare into the quiet water in companionable silence.

After a while, Erwin finds his foot being lifted up by the fin of Levi's tail. The merman brings the limb to himself and grabs it for closer scrutiny. Usually feet aren't something Erwin considers all that exciting, but to Levi it has to be a novelty. With intense concentration (that Erwin suspects is a parody of himself), Levi pinches a toe between his fingers and moves it back and forth. Unable to stifle the laughter this time, Erwin can't help but giggle as the tickling gets too much to bear. Levi looks up at the sound but quickly satisfies himself that it's not one of aggression and continues his intent research of human legs. If the toes had been weird then the thick hair he finds when he reaches the calf sends Levi's eyebrows up in genuine surprise. Petting the hair and feeling their coarseness a look of bewilderment settles on him. It isn't until now that Erwin realises there isn't a single hair on Levi except for on his head. It makes sense in accordance with evolution of course, considering how sleek skin provides better traction in water.

Levi lets out a huff of air from his nose and if Erwin hadn't known better he would have thought it a laugh. With another huff Levi shoves the leg away from himself and shakes his head, but the corners of his mouth is turned upwards.

It becomes a new routine for Erwin to visit Levi during his surveillance shifts and he knows he should be worried when he feels his heart skip a beat every time he finds Levi already waiting for him. Most nights his little merman is either fiddling with one of his possessions or trying to get his hair in some type of order.

“Sure we shouldn't cut it?” Erwin suggests one night when he finds Levi struggling to get the comb through the long tresses. Levi ignores him, now busy with his task and not in the mood to entertain him. It isn't until Erwin grabs the comb out of Levi's hand that the merman finally turns to him with a frown. Erwin merely twirls his finger to indicate that Levi is to turn back around before having a go at the knots. It is curious that Levi's hair is so much like a _homo sapien sapien's_ when it would have made more sense for it to be sleek and workable in water. But by the way Levi sits patiently as Erwin grooms him, it obvious that this is something mermaids do for each other. Social grooming, a common trait in both humans and apes and obviously then _homo sapiens sirens_ as well.

“I still don't know how to braid,” Erwin warns him, “Petra says I am a disgrace.” Levi shrugs one shoulder like he understands what Erwin is saying, but doesn't care much. These easy back and forths between them has Erwin's mind racing: how much has Levi already picked up?

“What do you think?” Erwin prompts again and tugs lightly at Levi's hair, “should we cut it or are you fine like this?” Levi looks up at Erwin from over his shoulder and blinks slowly, something Erwin has learned now is an indicator that he is paying special attention. Again Erwin takes Levi's hair and lets the long, wet strands fall through his fingers before brushing his hand through his own short cut, showing Levi how easy it is.

Though even if it is more practical, then Levi's hair is truly beautiful the way it is. If it doesn't bother him then Erwin would be happy to let it be. Turning around, Levi reaches up to touch Erwin's hair with both hands, carving his hands through it several times. Erwin can't help but notice even in the dimmed light of the hangar how Levi's ears have turned a brilliant blue again. This beautiful creature that seem as mesmerized by Erwin as he is with Levi in turn.

With his arms resting on Erwin's shoulders and hands tightly knotted in his hair, Levi has somehow moved close enough for their chests to brush against each other. There is no doubt in Erwin's mind now that Levi knows exactly how intimate this is. In the half-dark with the water glittering as it moves with the soft strokes of Levi's tail, it is easy for Erwin to forget where he is or what his role is. There is nothing but the silver of Levi's eyes, the soft pink of his lips and his breath brushing over Erwin's mouth.

He remembers well the sharp teeth that burried themselves in his flesh, but despite that tinge of fear, Erwin leans in the rest of the distance and gently brushes his lips against Levi's. They're as soft as they look and the way Levi kisses him back, how his lips move across his own without hesitation, it's clear that this is an intimacy he's used to. Wrapping his arms around the smaller merman, Erwin pulls him in even closer. The scent of saltwater envelopes him and it has his heart beating faster. It doesn't remind him of summers by the beach or the many years he's spent working in the lapping waves- all he can see in his mind's eye is Levi's graceful body twisting in the water, the glimmer of his scales nearly blinding.

There is no hesitation from Levi, no shyness or indication of what they're doing is giving him pause. Angling his head, Levi slowly sucks Erwin's bottom lip in between his own and Erwin's worry of those sharp predator teeth surfaces again, but is quickly forgotten. The skin underneath his hands is smooth and soft, the bunching muscles taut- these familiar sensations mixed with the completely alien sends new chills down his spine just as his chest and abdomen flares red hot with desire. A hushed sound escapes him, something between a hum and a moan. He's in completely unknown territory and it feels like he is at the edge of a breakthrough. Having spent years searching the ocean for new discoveries, Erwin has finally found it and it's here in his embrace, clutching him in a grip so strong he would have been afraid if he didn't want it so badly.

When Levi opens his mouth and laps a wet trail over Erwin's mouth the hairs on his arms raise up. It doesn't feel anything like a human tongue and now Erwin's curiosity has replaced any sense of fear while he lets his own tongue brush against Levi's. The texture is more leathery and sleek- unlike the soft muscle of a human. The merman likewise hesitates for a moment, probably coming to terms with Erwin's otherness. It only lasts for a heartbeat before the merman must have decided he doesn't mind it and he returns to the kiss with renewed passion. Levi is leading the kiss as he plunges deep into Erwin's mouth to taste and discover. The sound of water dripping is followed by Levi's tail coiling around the both of them, bringing them even closer and Erwin knows that he couldn't have escaped now even if he had wanted to. And he really doesn't want to.

Time is an abstract thing and now it feels like it has ceased entirely as they sit wrapped up in each other there in the dark. Levi's skin that is always so cold to the touch is heating up and his breath sounds laboured. Somewhere in the back of his mind Erwin is worried about the extended time Levi has been out of the water, but Levi himself doesn't seem like he's about to stop any time soon. Yet the spell is broken and Erwin remembers where he is and what he is supposed to be doing. It takes a couple of tries of pulling on Levi's arm to loosen it from its grip before he has Levi's attention. With a small sigh, Levi leans back enough that he's able to look up into Erwin's face, but whatever he sees there puts him on edge and the familiar scowl is back.

“I have to go,” Erwin whispers and he realises he's nearly out of breath himself. “Hanji is next on shift and they really can't find us like this.”

Whether Levi understands the words or not is hard to decipher, but the merman purses his lips and looks away, his silver eyes reflecting the muted lights. An apex predator of the ocean here in Erwin's arms.

Against his better instincts that are now finally fluttering its wings inside Erwin's stunned mind, he cups Levi's face and places a soft kiss on his forehead. Silence descends and it is of the deep kind, the uncomfortable one born out of frustration and all the words they want to convey but falls dead between them. Eventually Levi unwraps his tail and in one fluid motion drops back into the dark water.

The next few nights and days move in a grey haze. Erwin doesn't sleep, but neither does he visit Levi during his shifts anymore. Instead he has thrown himself full into work, vision blurred and heart racing from fatigue. The nights are spent running for hours on the treadmill. The relationship between them has become strained- Levi no longer jumps up on the grate to meet him and seems to have lost his will to play pranks on the others. Mike expresses a relief that he hasn't gotten a bucket of water dropped on him for a while, but the crease between Hanji's brow is deepening.

Erwin wishes he could tell Levi exactly why he is keeping his distance. That he's confused and a little bit afraid at his own attraction towards him. Not only is it inappropriate for a man in his position to engage in intimate relations with the ward in his care, but they aren't even the same species. Most probably Levi understands the latter, maybe even has the same reservations, but the former would be all too difficult to convey without words.

It is early morning, though Erwin no longer has a sense of night and day- he hasn't been to the surface since Levi arrived. He is starting to feel trapped, suffocated, and he can only imagine what Levi is going through. With clipboard in hand, Erwin is standing in front of the tank trying to fill in Levi's stats:

**Code:** Specimen 01 (Levi)

**Species:** Homo sapiens siren

**Age:** Unknown

**Full length:** 264 m

**Tail length:** 177m

**Weight:** 194 kilo

**Blood type:** Unknown – temp. ID “Pi ( _Π)”_

**Hair colour:** Black

**Eye colour:** Grey (silver)

**Distinguishing marks:** A scar from forehead to corner of mouth, right side.

The list goes on and on asking for stats, growth, progress as well as setbacks. Erwin fills it out diligently on the first of every month, but there is little to no changes. Levi's grudging cooperation has allowed for more of the brackets to be filled in, such as weight and length. Of course Erwin doesn't report on just how close he has gotten to Levi and makes sure to keep his language neutral. At least he tries, though he suspects the change in his attitude towards specimen 01 is apparent for anyone who wants to find it.

There's a buzzing from the telecom by the lift, but Erwin ignores it. It is probably just mail and groceries and Nana is usually the one to get those. In the tank, Levi has his back to Erwin, busy with one of his projects. Lately he's been moving the smaller rocks around and rearranging them. It is easy to forget the strength the small merman possesses and even if Erwin is fully aware of it, has been intimately close to it more than once, he's surprised all over again when Levi flips over a boulder nearly the same size as himself.

The sounds of the hangar are all familiar and easy to filter out as he frowns down at his papers. These notes that are all revolutionary, that will change how the entirety of humanity views the ocean and the world around them. And yet all he wants to do with them is to tear them into pieces. It doesn't matter how carefully they craft their research papers, how meticulous they are in precenting the evidence, Erwin knows exactly how humanity will react. There will always be those possessing curiosity and compassion towards their ocean kin, but money talks louder than any of their voices and it doesn't matter just how sentient another creature is. Whales and dolphins are excellent examples of humanity's cruelty.

Lost in his own crowded mind, it isn't until Nana is tapping him on the shoulder that Erwin looks up.

“Dr. Dok is here with team B,” Nana informs him, the pinch around her mouth conveying her thoughts in that regard.

Erwin doesn't have time to turn around before the all too familiar voice echoes through the hangar, “long time no see, Erwin!”

“Nile,” Erwin greets him in turn with a nod and a small smile that isn't in the least bit genuine. Having Nile and his team around now is about as bad as it can get.

“So this is it, huh...” Nile ignores Erwin's lukewarm greeting to lay his full attention on the tank and the one who inhabits it. Erwin has known Nile since their days at university, but he can safely say he has never seen the man like this. Eyes round and cheeks flushed, there is no denying the reverence he must be feeling at seeing this creature up close for the first time. Even Erwin is still overcome with wonder every time he enters the hangar and sees Levi. It doesn't matter that he's seen him every day for several months.

It wouldn't be apparent for the new scientists that Levi has even noticed their arrival. He continues with his work undisturbed, but Erwin can see in the way his tail moves with sharp strokes rather than languid ones and how his caudal fins are gradually changing their hue to a dark blue. He's very much aware that something is happening, but like most predators he is pretending ignorance until he can pounce.

The rest of team B has gathered around the tank, most of them slack jawed and wide eyed, but Erwin could hardly blame them. At the edges hovers Nana, Hanji, Mike and Petra with expressions ranging from anxious to down right hostile. This project has been their entire life for such a long time it is easy to forget that they're not alone on it. All of them, with the only exception of Erwin himself, could be exchanged with members of team B at any moment. Of course, there would have to be a good reason for such a switch so Erwin hopes they'll all remain on their best behaviour. Throwing Hanji an especially pointed look, he is met with a sour grimace and a rude finger from the highly decorated doctor.

“Having read the reports and seeing it in real life are two very different things,” Nile breathes and Erwin knows exactly what he's feeling; this is the culmination of all his ambitions, the crowning jewel of his career and his purpose of living. Just like it was Erwin's.

Team B are already busy furiously writing down notes on their iPads and one raises his phone to take pictures.

“No flash!” Erwin barks, pushing down on the compulsion to take the phone and crush it underneath his heel. Thankfully there is no need to because the young man startles and drops his phone, the crack of its screen audible to them all. Scrabbling for his phone, the young man looks up at Erwin with shock on his face, but Erwin has no sympathy for him and turns away to check on Levi.

“It's building something?” someone pipes up between hurried scribbling.

“Yes, he's been at it for a couple of days now,” Erwin replies and it isn't until Nile gives him a pointed look that he realises his slip up in pronouns.

“I admire the work you've been doing here, I really do,” Nile says and for once he actually sounds genuine, “but Erwin, if we are to do _our_ part of the job we need a little more than stale reports. We need blood and tissue samples, DNA swabs, you name it. I mean you haven't even been able to establish its age yet...”

“There's a reason I am heading team A and not you,” Erwin reminds him coolly, “you'll get your samples as soon as we're done with them here.”

Placing his arm around Erwin's shoulders like they haven't been competing academically for ten years, Nile leans in close and smiles unconvincingly, “now don't be such a dick, Erwin-”

A loud thunk right by Erwin has all of them jumping back, several with a shout of surprise and fear. Levi has his fists against the glass of the tank and his eyes are trained on Nile with undisguised hostility. There is absolutely no doubt in Erwin's mind that if Levi got his hands on Nile, he'd snap his neck. He hasn't seen that glare since the first evening Levi arrived.

“What is it doing?” one of team B asks the room in general. They've all taken several more steps back despite knowing that short of a bulldozer, little else would be able to break that glass.

“Le- the specimen is not too fond of new people,” Erwin explains. The statement is true, of course, but he suspects that's not it this time. The confusion could be to his advantage though, “I'm afraid your presence here might have set us back quite a bit actually, Nile.”

And while Erwin have butted heads against his scholarly nemesis more than once, he knows that Nile is a pretty clever guy. His brown eyes moves slowly from Levi's glare to Erwin and then back again. For a while he stands there stroking his goatee and it feels like an age. Every muscle in Erwin's body aches to move in between Levi and Nile to shield the merman from them, but right now that would make it so much worse and so Erwin digs his nails into the palm of his hand instead.

“Erwin is probably right,” Nile finally acquiescents, “we shouldn't all have trooped up here without anticipating agitation from specimen 01, the reports from its first days here made that clear and this was an error in my judgement.”

When Erwin sees the crestfallen look of team B and the gloating grins from team A, he barely manages to keep back his own laughter. Despite wanting to boot the lot of team B out, they _are_ their guests and there are certain etiquettes you just don't break in academia.

“There is tea and coffee in the kitchen,” Erwin informs them like the gracious host that he is before turning to Nile, “I'll have to finish up here, then we can have a proper talk in my office. There are a few things we need to clear up in our collaboration.”

“On that I certainly agree with you,” Nile replies and gives Levi one last critical look before he follows his team out of the hangar area.

With the hangar empty except Nana who is busy working on a new contraption to easier monitor Levi's weight and heart rate, Erwin walks up to the tank and looks up at the merman. The pale, heart shaped face is still, but his eyes are like cutting steel. What happened in the moment Nile touched Erwin is something that neither of them prepared for: jealousy.

Even if Erwin would have wanted to remain at a distance until these emotions began to fade, it is no longer only his decision to make.

“ _I found Levi engrossed with Mike and Nana today in a game of cards. It had been Nana's idea to order in waterproof playing cards to see if Levi has the type of object permanency that would allow him to learn simple rules and strategies. Not only did Levi pick up on it quickly, he won nearly every match and Mike was seething. I couldn't help but note Levi's pleased huff when Mike threw the cards down in defeat._ ”

Nile drops the papers down on Erwin's desk after he's finished reading them out loud. Erwin has just arrived at his office only to find that Nile is already occupying it. No, when his journal is read back to him like this, Erwin realises that he's been anything but neutral. Slowly, Erwin closes the door behind them. Deep down in the bunker every room is sound proof.

“This piece of writing is certainly a far cry from the droll reports _I_ get from you,” Nile shrugs nonchalantly and settles down in the other chair occupying Erwin's office. “You've developed quite an intricate personality for specimen 01.”

Confused by the last statement, Erwin covers his hesitation by demonstratively cleaning up his private papers and dumping them in the drawer they should have been in. Under lock and key.

“I haven't developed anything, Levi is Levi,” Erwin replies after a while. He remains standing by his desk. He is not giving any ground here.

“It's a nice name,” Nile hums. His hand is back to stroking his goatee in the way he does when he's thinking furiously.

When Nile finally looks back at Erwin it is with widened eyes as if the conclusion he just reached boggles even his mind. There is no way he truly knows the extent of Erwin and Levi's relationship and so Erwin remains calm, keeping his cards close to his chest. That he's grown attached to his ward is not strange, it happens all the time in their field of work, but Levi's response to it is cause for pause...

“That you've given it a name and everything is not surprising,” Nile says, echoing Erwin's thoughts, “what concerns me is the lousy ass reports you've been giving _me_ , how you've been stinting the test samples, no picture or video documentation- honestly, it has all been a huge waste of my time. I figured it was taking its sweet time because the specimen was uncooperative, but reading that piece of text I figure, _hm_ , Erwin sure is holding out here.”

Erwin knows that now is not the time to hesitate. This can be twisted to his own advantage.

“So I want my name top, front and centre on this project,” Erwin retaliates, “what else is new?”

“And you really imagine I will let you do that? Just roll over and play nice?” Nile shoots back, used to these stalemates between them. “You know what, I'll give you a deal for old times sake: you send me copies of your journal as well as the proper materials we need, and I won't file a report on you declaring you unfit to govern this project neutrally.”

Usually Erwin doesn't really have a hard time reining in his temper, but Nile just has a way of needling himself under his skin in the worst way possible. Throwing composure to the wind, Erwin leans over the desk and grabs Nile by the front of his shirt and hoists him up from the chair.

“Now listen here you piece of shit,” he growls into the very startled face, “if you get in the way of this in any way I _will_ destroy your career and you know I am fully capable of doing so.”

Once the initial shock has settled, Nile's face darkens and he manages to wrench himself loose of Erwin's grip. “Seriously, you fucking asshole,” Nile swears as he tries to put his rumpled shirt back in order. “People think you're this genius scientist but you're really just a megalomaniac.”

Erwin brushes blonde hair away from his face with a hand that's shaking from the anger still coursing through him and the fear of what this thinly veiled conversation is actually about. That Levi might end up in someone else's hands and that his existence will be revealed to the unforgiving light of media scrutiny.

“Just leave him alone.” The words are out of Erwin's mouth before he can stop them. Their eyes lock, but Erwin is not going to back down.

“Ah,” Nile smiles softly. That never bodes well. With his brow furrowed, Nile rests his hands on his hips and chews on his lip for a moment. “I have this proposal then: I come here about once or twice a week and do my own study and take my own tests-” Nile holds his hand up as Erwin draws in breath to protest, “- but we can file my findings here together with yours. I should have been on team A to begin with anyway, so this only makes sense. I want my name on that god damned paper Erwin.”

Erwin lets his arm fall down by his side and a wide grin creeps across his face. It is not a pleasant expression.“Sure Nile, we can manage that.”

“I've said all these years there's something seriously wrong with you, but whatever,” Nile grouses and holds out his hand. Erwin takes it and they shake on their new agreement.

**Author's Note:**

> ❤️


End file.
